MAX1233/MAX1234
±15kV ESD-Protected Touch-Screen
Controllers Include DAC and Keypad Controller
34 ______________________________________________________________________________________
Battery Voltage, Auxiliary Input, and
Temperature Input Scan
Use this scan to make periodic measurements of both
battery inputs, both auxiliary inputs, and both tempera-
ture inputs. The respective data registers have the lat-
est results at the end of each cycle. Thus, a single write
by the host to the MAX1233/MAX1234 ADC control reg-
ister results in six different measurements being made.
Figure 20 shows this scan operation.
Touch-Initiated Screen Scans
(PENSTS = 1; ADSTS = 0)
In the touch-initiated screen-scan mode, the
MAX1233/MAX1234 automatically perform a touch-
screen scan upon detecting a screen touch. The touch-
screen scans performed are determined by the
[A/D3:A/D0] written to the ADC control register. Figure
21 shows the flowchart for a complete touch-initiated X-
and Y- coordinate scan. Selection of resolution, conver-
sion rate, averaging, and touch-screen settling time
determine the overall conversion time.
Figure 22 shows the complete flowchart for a touch-
initiated X, Y, and Z scan.
Table 38 shows ADSTS Bit Operation.
Host-Initiated Screen Scans
(PENSTS = ADSTS = 0)
In this mode, the host processor decides when a touch-
screen scan begins. The MAX1233/MAX1234 detect a
screen touch and drive PENIRQ LOW. The host recog-
nizes the interrupt request and can choose to write to
the ADC control register to select a touch-screen scan
function (PENSTS = ADSTS = 0). Figures 23 and 24
show the process of a host-initiated screen scan.
Key-Press Initiated Debounce Scan
(KEYSTS1 = 1, KEYSTS0 =0)
In the key-press initiated debounce mode, the
MAX1233/MAX1234 automatically perform a debounce
upon detecting a key press. Key scanning begins once
a key press has been detected and ends when a key
press has been debounced (Figures 25 and 9a).
Host-Initiated Debounce Scan
In this mode, the host processor decides when a
debounce scan begins. The MAX1233/MAX1234 detect
a key press and drive KEYIRQ low. The host processor
recognizes the interrupt request and can choose to
write to the keypad control register to initiate a
debounce scan (Figures 26 and 9b).
Keypad Debouncing
Keys are debounced either when (1) a key press has
been detected, or (2) when commanded by the host MPU.
The keys scanned by the keypad row and column pins
are debounced for a period of time (debounce period)
as determined by bits [DBN2:DBN0] of the keypad con-
trol register.
The keypad controller continues scanning until the keypad
stays in the same state for an entire debounce period.
Keypad Data
Keypad data can be read out of either the keypad data
status register (maskable), or the keypad data pending
register (not maskable). The keypad mask register is
used to mask individual keys in the keypad data status
register.
GPIO Control
Write to bits [GP7:GP0] of the GPIO control register to
configure one or more of the R_/C_pins as a GPIO pin.
Write to bits [OE7:OE0] of the GPIO control register to
configure the pins as an input or an output. GPIO data
can be read from or written to the GPIO data register. A
read returns the logic state of the GPIO pin. A write sets
the logic state of a GPIO output pin. Writing to a GPIO
input pin has no effect.
GPIO Pullup Disable Register
When programmed as GPIO output, by default, the
GPIO pins are active CMOS outputs. Write a 1 to the
pullup disable register to configure the GPIO output as
an open-drain output.
Using the 8-Bit DAC for LCD/TFT
Contrast Control
Design Example:
The 8-bit DAC offers the ability to control biasing of
LCD/TFT screens. In the circuit of Figure 27, it is
desired to have the MAX1677 DC-DC converter’s V
OUT
to be adjustable.
The minimum and maximum DAC voltages (V
DAC(HIGH)
and V
DAC(LOW)
) can be found in the
Electrical
Characteristics
table.
The output voltage of the MAX1677 (V
OUT
) can be cal-
culated by noting the following equations:
V
OUT
= V
REFDAC
+ i
1
R1 [Equation 1]
i
1
= i
2
+ i
3
[Equation 2]
i
2
= V
REFDAC
/ R2 [Equation 3]
i
3
= (V
REFDAC
- V
DAC
) / R3 [Equation 4]
Substituting equations 2, 3, and 4 into equation 1
yields:
V
OUT
= V
REFDAC
+ (R1 / R2) V
REF
+ (R1 / R3)
(V
REFDAC
- V
DAC
) [Equation 5]
